.TH std::ranges::uninitialized_copy,std::ranges::uninitialized_copy_result 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::uninitialized_copy,std::ranges::uninitialized_copy_result \- std::ranges::uninitialized_copy,std::ranges::uninitialized_copy_result

.SH Synopsis
   Defined in header <memory>
   Call signature
   template< std::input_iterator I, std::sentinel_for<I> S1,

             no-throw-forward-iterator O, no-throw-sentinel-for<O> S2 >
   requires std::constructible_from<std::iter_value_t<O>,                   \fB(1)\fP (since
   std::iter_reference_t<I>>                                                    C++20)
            uninitialized_copy_result<I, O>

            uninitialized_copy( I ifirst, S1 ilast, O ofirst, S2 olast );
   template< ranges::input_range IR, no-throw-forward-range OR >

   requires std::constructible_from<ranges::range_value_t<OR>,
            ranges::range_reference_t<IR>>                                  \fB(2)\fP (since
            uninitialized_copy_result<ranges::borrowed_iterator_t<IR>,          C++20)
                                      ranges::borrowed_iterator_t<OR>>

            uninitialized_copy( IR&& in_range, OR&& out_range );
.SH Helper types
   template< class I, class O >                                             \fB(3)\fP (since
   using uninitialized_copy_result = ranges::in_out_result<I, O>;               C++20)

   1) Let \\(\\scriptsize N\\)N be ranges::min(ranges::distance(ifirst, ilast),
   ranges::distance(ofirst, olast)), constructs \\(\\scriptsize N\\)N elements in the
   output range [ofirst, olast), which is an uninitialized memory area, from the
   elements in the input range [ifirst, ilast).
   The input and output ranges must not overlap.
   If an exception is thrown during the initialization, the objects already constructed
   are destroyed in an unspecified order.
   The function has the effect equal to:

 for (; !(ifirst == ilast || ofirst == olast); ++ofirst, ++ifirst)
 {
     ::new (static_cast<void*>(std::addressof(*ofirst)))
         std::remove_reference_t<std::iter_reference_t<O>>(*ifirst);
 }

   2) Same as \fB(1)\fP, but uses in_range as the first range and out_range as the second
   range, as if using ranges::begin(in_range) as ifirst, ranges::end(in_range) as
   ilast, ranges::begin(out_range) as ofirst, and ranges::end(out_range) as olast.

   The function-like entities described on this page are niebloids, that is:

     * Explicit template argument lists cannot be specified when calling any of them.
     * None of them are visible to argument-dependent lookup.
     * When any of them are found by normal unqualified lookup as the name to the left
       of the function-call operator, argument-dependent lookup is inhibited.

   In practice, they may be implemented as function objects, or with special compiler
   extensions.

.SH Parameters

   ifirst, ilast - iterator-sentinel pair denoting the range of elements to copy from
   in_range      - the range of elements to copy from
   ofirst, olast - iterator-sentinel pair denoting the destination range
   out_range     - the destination range

.SH Return value

   {ifirst + N, ofirst + N}

.SH Complexity

   \\(\\scriptsize\\mathcal{O}(N)\\)𝓞(N).

.SH Exceptions

   The exception thrown on construction of the elements in the destination range, if
   any.

.SH Notes

   An implementation may improve the efficiency of ranges::uninitialized_copy if the
   value type of the output range is TrivialType.

.SH Possible implementation

   struct uninitialized_copy_fn
   {
       template<std::input_iterator I, std::sentinel_for<I> S1,
                no-throw-forward-iterator O, no-throw-sentinel-for<O> S2>
       requires std::constructible_from<std::iter_value_t<O>, std::iter_reference_t<I>>
       ranges::uninitialized_copy_result<I, O>
       operator()(I ifirst, S1 ilast, O ofirst, S2 olast) const
       {
           O current{ofirst};
           try
           {
               for (; !(ifirst == ilast or current == olast); ++ifirst, ++current)
                   ranges::construct_at(std::addressof(*current), *ifirst);
               return {std::move(ifirst), std::move(current)};
           }
           catch (...) // rollback: destroy constructed elements
           {
               for (; ofirst != current; ++ofirst)
                   ranges::destroy_at(std::addressof(*ofirst));
               throw;
           }
       }

       template<ranges::input_range IR, no-throw-forward-range OR>
       requires std::constructible_from<ranges::range_value_t<OR>,
                ranges::range_reference_t<IR>>
       ranges::uninitialized_copy_result<ranges::borrowed_iterator_t<IR>,
                                         ranges::borrowed_iterator_t<OR>>
       operator()(IR&& in_range, OR&& out_range) const
       {
           return (*this)(ranges::begin(in_range), ranges::end(in_range),
                          ranges::begin(out_range), ranges::end(out_range));
       }
   };

   inline constexpr uninitialized_copy_fn uninitialized_copy{};

.SH Example


// Run this code

 #include <cstdlib>
 #include <iomanip>
 #include <iostream>
 #include <memory>
 #include <string>

 int main()
 {
     const char* v[]{"This", "is", "an", "example"};

     if (const auto sz{std::size(v)};
         void* pbuf = std::aligned_alloc(alignof(std::string), sizeof(std::string) * sz))
     {
         try
         {
             auto first{static_cast<std::string*>(pbuf)};
             auto last{first + sz};
             std::ranges::uninitialized_copy(std::begin(v), std::end(v), first, last);

             std::cout << "{";
             for (auto it{first}; it != last; ++it)
                 std::cout << (it == first ? "" : ", ") << std::quoted(*it);
             std::cout << "};\\n";

             std::ranges::destroy(first, last);
         }
         catch (...)
         {
             std::cout << "uninitialized_copy exception\\n";
         }
         std::free(pbuf);
     }
 }

.SH Output:

 {"This", "is", "an", "example"};

   Defect reports

   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.

      DR    Applied to              Behavior as published              Correct behavior
   LWG 3870 C++20      this algorithm might create objects on a const  kept disallowed
                       storage

.SH See also

   ranges::uninitialized_copy_n copies a number of objects to an uninitialized area of
   (C++20)                      memory
                                (niebloid)
                                copies a range of objects to an uninitialized area of
   uninitialized_copy           memory
                                \fI(function template)\fP
